1. Technical Field
The embodiments herein generally relate to microelectronic systems, and, more particularly, to radio frequency (RF) microelectromechanical systems (MEMS) switches.
2. Description of the Related Art
RF MEMS switches have recently received considerable attention. Generally desirable for their extremely low insertion loss, extreme linearity, minimal intermodulation product generation, and power consumption characteristics; RF MEMS switches posses many advantages over their competing technologies. RF MEMS switches fall into two basic categories: series/shunt RF configurations, and ohmic/capacitive contact behaviors. RF MEMS series switches have been demonstrated with both ohmic and capacitive contacts.
However, the majority of RF MEMS shunt switches have been configured with capacitive contact architectures. Many successful switches of this kind have been demonstrated over the years but, generally, all inherently suffer from inadequate performance below X-band (<10 GHz) and are subject to their own failure mechanisms.
DC-contact, or ohmic. RF MEMS shunt switches have also been demonstrated. These switches utilize a free, hinge-constrained, contact beam with separate actuation pads. However, physical contact still occurs between the actuation electrodes and the contact beam; an undesirable trait with respect to switch lifetime. The inductance of such a design also tends to hamper the high frequency operation of the switch. Moreover, the lack of rigid mechanical constraints within the hinge region tends to make this design exceedingly susceptible to performance degradation due to vibration or even simple rigid body motion of the parent system and limits its attainable switching speed. The lack of rigid mechanical constraints within the hinge region also, in all likelihood, results in significant device-to-device performance variability. All of these factors tend to limit the operational lifetime of the switch as well as its usefulness in military applications.
Other designs use a DC-contact RF MEMS shunt switch that utilizes a suspended RF center conductor contact beam. Bias electrodes are placed directly beneath this structure to enable maximum (with respect to geometric considerations of load application only) actuation force/unit voltage. This design prevents direct physical contact between the actuation electrodes and the contact beam. However, to attain this feature with the suspended RF center conductor contact beam design, the actuation electrodes must be present in the co-planar waveguide (CPW) gaps. This leads to significant degradation in the return loss of the switch, particularly at higher frequencies. The presence of this metal in the CPW gaps prevents proper impedance matching over a large range of frequencies and contributes to low return loss. Accordingly, there remains a need for a new electrostatic ohmic shunt RF MEMS switch that achieves an improved insertion loss performance over conventional switches.